Reconstructing deep-sea oxygenation in the Western Alboran Sea Basin during Late Pleistocene-Holocene (last 37 kyrs): Insights from a multiproxy approach.

Abstract

A deep-sea sediment record from the Western Alboran Basin spanning the last 37 kyr has been analysed using a multiproxy approach, integrating sediment colour, magnetic susceptibility, elemental ratios, benthic foraminiferal assemblages and bioturbation gaining new insights into Alboran Basin deep-sea environments and palaeoceanographic conditions since the Last Glacial Maximum. The combination of a diverse set of proxies made it possible to recognize the diagenetic signals and reconstruct new low-frequency events in the deep basin, recording the significant fluctuations in deep water oxygenation occurred during the studied period. From the studied data, short-term periodic low-oxygen events are recognised during Heinrich Stadials 2 and 3 (HS2 and HS3) and Greenland Interstadial GI8, showing important responses of the deep sea environments to climate low frequency climate change. Furthermore, the presence of a not previously well-defined Organic Rich Layer 2 (ORL 2) can be defined from the observations, being able to define it as a concatenation of events transitioning between low oxygen (associated with humid conditions and Heinrich Events) and oxygenated conditions, and not as a singular low oxygenation event. In addition, the Organic Rich Layer 1 (ORL1), associated with the most recent low oxygen event has been also recognised in the record, with low oxygen conditions starting as early as 16 kyr before the present (BP) during the HS1 and spanning to 8 kyr BP with important fluctuations in environmental conditions and oxygenation. Several climate events that have been previously recognised in the Northern Hemisphere and in the Mediterranean Basin can be linked to the observed changes in oxygen conditions during ORL1 deposition, for instance reoxygenation that occurred during the pre-ORL1, between the demise of Heinrich Event 1.1 (HE1.1) and the end of HS1 and the inception of the Bølling-Allerød (BA); the start of ORL1 deposition during BA with the onset of low oxygen conditions. Interestingly, the BA is punctuated by short duration reoxygenation events that can be recognised in the record and correlated to cold events observed in the North Atlantic records. Also, there is a partial discontinuous reoxygenation during the Younger Dryas (YD), observed also in the Eastern Mediterranean and in other Mediterranean sites which was followed by the return to loweroxygen conditions after the YD, coinciding with the start of S1 deposition. Finally, the final reoxygenation event occurs at around 8 kyr BP along with the demise of the ORL1.